php form with select option "Other"

[phpbegginer]

hello,

i have to create a php form, where there is multiple selection on the select option, when we select other, how to get a visible text box where user can key in the other description?

sample of code need to alter.


<form id="form1" name="form1" method="post" action="<?=$_SERVER['PHP_SELF'];?>">

<p>
<select name="select">
<option value="please select one">Please select one</option>
<option value="car">car</option>
<option value="bike">bike</option>
<option value="other">other</option>
</select>
<input type="text" name="textfield">
</p>
<p>
<input type="submit" name="Submit" value="Submit" />

</p>
</form>